Iran accused world powers on Tuesday of dragging their feet in negotiations over its nuclear activities, as both sides were about to hold a new, downgraded round of talks in Istanbul.

Foreign ministry spokesman Ramin Mehmanparast told a weekly briefing that, if the powers ignored Iran's nuclear "rights" and failed to bargain on equal terms, the negotiations could lead to an "impasse".

"All that can reinforce the idea that there is a desire to drag out the negotiations or prevent their success," he said.

He also said to reporters after the briefing that "illogical, irresponsible" Western sanctions "amount to a hostile act against Iran and its national interests."

He added: "Iran will do its utmost to defend its national interests and territorial integrity."

Iran and the P5+1 group comprising the five UN Security Council permanent members (Britain, China, France, Russia and the United States) plus Germany were to hold an experts-level meeting in Istanbul to discuss efforts to curb Tehran's atomic activities.

The talks were to take place between technical experts after three previous rounds earlier this year, at a more senior political level, failed to bridge the vast gap dividing the two sides.

Iran is insisting it has a "right" to uranium enrichment under the nuclear Non-Proliferation Treaty, and that that be recognised by the P5+1. It also wants Western sanctions punishing its economy to be eased.

The P5+1 instead is pushing for an immediate end to Iran enriching uranium to 20 percent purity -- just a technical step short of the 90 percent needed to make nuclear bombs -- and to ship out its existing 20-percent stock and close a fortified underground enrichment facility in Fordo.

Mehmanparast said the P5+1's negotiating position and the Western sanctions suggested that maybe the world powers did not want to see the talks bear fruit.

"Many people are starting to conclude that maybe there are specific goals in dragging out the talks and preventing their success. One option is that perhaps there is a link with the US (presidential) election" in November, he said.

He said the "illegal" sanctions contradicted the West's affirmation that it wants to resolve the standoff diplomatically.

He reiterated his government's message that the sanctions would not coerce it into a change of position.